This invention relates generally to aircraft gas turbine engines, and more specifically to counter-rotating gas turbine engines.
At least one known gas turbine engine includes, in serial flow arrangement, a forward fan assembly, an aft fan assembly, a high-pressure compressor for compressing air flowing through the engine, a combustor for mixing fuel with the compressed air such that the mixture may be ignited, and a high-pressure turbine. The high-pressure compressor, combustor and high-pressure turbine are sometimes collectively referred to as the core engine. In operation, the core engine generates combustion gases which are discharged downstream to a counter-rotating low-pressure turbine that extracts energy therefrom for powering the forward and aft fan assemblies. Within at least some known gas turbine engines, at least one turbine rotates in an opposite direction than the other rotating components within the engine
At least one known counter-rotating low-pressure turbine has an inlet radius that is larger than a radius of the high-pressure turbine discharge. The increased size of the inlet radius enables the low-pressure turbine to accommodate additional stages. Specifically, at least one known counter-rotating low-pressure turbine includes an outer turbine having a first quantity of low-pressure stages that are rotatably coupled to the forward fan assembly, and an inner turbine having an equal number of stages that is rotatably coupled to the aft fan assembly.
During operation, lubrication is supplied to the forward and aft fan assemblies and to the low-pressure turbine utilizing a relatively complex lubrication system. Such lubrication systems are designed to supply lubricating fluid to a plurality of bearings supporting the forward and aft fan assemblies and the low-pressure turbine, for example. However, to lubricate the forward and aft fan assemblies and the low-pressure turbine, at least one known gas turbine engine is configured to channel the lubricating fluid around the plurality of rotating components that are rotating in opposite rotational directions. Accordingly, designing and implementing a lubrication system capable of lubricating the forward and aft fan assemblies and an low-pressure turbine within a counter-rotating gas turbine engine may result in increasing the overall weight of the gas turbine engine which may cause an associated increase in the costs of manufacturing and assembling the gas turbine engine.